This invention relates to an apparatus for generating hydraulic shock waves in an oil, gas, or water bearing formation, and more particularly to such apparatus including a tool that may be lowered within a well from an electrical cable and provide an electrically generated shock wave for the recovery of fluids, such as crude oil, gas or water.
Heretofore, various processes and apparatus have been provided for the recovery of crude oil by means of sonic wave generations. The generation of a sonic wave front at or near an oil bearing formation provides sonic energy projecting a substantial distance into the formation for stimulating the recovery of oil from the formation particularly at adjacent wells. Sonic waves may be produced from shock waves resulting from the release of electrical energy adjacent the oil bearing formation and it is desirable to release substantial electrical energy in order to generate the intensity of shock or pressure waves required for a substantial recovery of oil or gas. Some of the disadvantages associated with the use of sonic and ultrasonic energy at both high and low frequency ranges are (1) high frequency waves attenuate too quickly in the formation and (2) low frequency waves at high amplitudes release debris which tends to restrict flow around the wellbore.
Electrical energy has been previously employed for the generation of shock waves for the recovery of oil. For example, U.S. Pat. No. 4,074,758 dated Feb. 21, 1978 shows a method and apparatus utilizing an electrical energy storage capacitor bank to provide electrical energy to a shock wave generator adjacent an oil bearing formation and having a pair of discharge electrodes forming a spark gap therebetween. An electrohydraulic shock wave is generated by liquid in the well from a shock wave generator lowered within the casing to a desired depth.
U.S. Pat. No. 4,345,650 dated Aug. 24, 1982 also shows a method and apparatus utilizing electrical energy to provide a shock wave at the oil bearing formation. However, the '650 patent utilizes a tool having an electrical energy storage capacitor bank therein adjacent the electrodes in the borehole to provide sufficient electrical energy. A relatively complex downhole tool is required, however, in order to house the storage capacitor bank and associated equipment shown in this patent for generating the explosive spark across the electrodes.
As well known, when electrical energy of a high voltage, such as 75000 volts or higher, is required downhole, power surges occur in the system from electrical energy flowing both down into the borehole and up from the borehole. Such power surges oftentimes result in overloading of the system and actuation of overload safety devices. The '650 patent minimizes this problem by locating the storage capacitor bank downhole.